Spectroscopy ofMn4+-doped Ca-substituted gadolinium gallium garnet

Abstract

The results of optical studies of Ca- and Mg-substituted ${\mathrm{Gd}}_3$ ${\mathrm{Ga}}_5$ ${\mathrm{O}}_{12}$ garnets doped with ${\mathrm{Mn}}^{4+}$ are reported. Multiple sites of ${\mathrm{Mn}}^{4+}$ ions are revealed at liquid-helium temperature by laser excitation and emission spectra and analysis of decay kinetics. Use of different charge-compensating ions allows one to obtain information on the nature of some sites occupied by the ${\mathrm{Mn}}^{4+}$ ions. A large Stokes shift between excitation and luminescence spectra of the ${}_{}{}^2{}_{}{}^{}$E state of ${\mathrm{Mn}}^{4+}$ ions is explained by interaction with low-energy lattice excitations. On the other hand, the higher-energy phonons are found to be responsible for nonradiative decay of the ${\mathrm{Mn}}^{4+}$ luminescence at higher temperatures. Charge-transfer states are present in the crystals examined.